October 17, 2010

The End Of Time?

by Sam Savage

A group of astrophysicists said the end of the world cannot be avoided, but it can be predicted, and see a 50/50 chance of the final countdown coming in about 3.7 billion years.

"Time is unlikely to end in our lifetime, but there is a 50 percent chance that time will end within the next 3.7 billion years," the team of US and Japanese scientists, who are challenging a long-standing theory of the universe, said.

While scientists have long concluded that the universe will continue to expand for an infinite period of time, the researchers say the very rules of physics suggest that the universe cannot continue to expand forever.

"The point of this paper is to show that certain methods and assumptions that have been widely used by physicists for years -- most prominently, the use of a time cutoff in order to compute probabilities in an eternally inflating universe -- lead to the conclusion that time will end," Raphael Bousso of the University of California, Berkeley told AFP.

"In other words, the time cutoff, which we may have thought was just a calculational tool, actually behaves like a physical event, whether we like it or not," said Bousso, lead author of the study.

Currently, theorists have assumed the universe, which began with the Big Bang 13.7 billion years ago, will simply expand forever, but have also used a speculative expiration date to help calculate the laws and rules of physics.

But Bousso and colleagues say the discipline cannot have it both ways. Although, he cautioned that calculations and research could not be used to come to a definitive conclusion.

"It's very important to understand that we are not saying that we are certain of the conclusion that time will end (though we cannot rule out that it may be correct)," he wrote.

But even if the theory was false, discovering why that was the case would help scientists better understand the universe, he wrote.

"In science, this kind of reasoning is often valuable: you realize that your reasonable-seeming theory predicts something that sounds crazy, so you have to come to grips with that," Bousso told AFP.

"Either you have to abandon the theory, or you have to understand why the crazy-sounding thing may not actually be so crazy," he added.

But for astrophysicist Charles Lineweaver, of Australian National University's Mount Stromlo Observatory, Bousso's calculations and conclusions are not accurate.

"Bousso's average life of a universe is a set time, only because that's what happens when you introduce a cutoff point to get a reasonable probability," he said, adding "it's a statistical technique being taken probably too seriously."

Bousso, though, said he and his team did not invent or introduce anything. "These cutoffs have been used by many leading physicists for years"¦ we merely pointed out that it's not such an innocent thing to do."

"The cutoff on time is inevitably physical and hence requires a physical justification. It cannot be considered a mere mathematical trick."